Parkinson's disease (PD) is a late-onset, progressive motor disease marked by relatively selective nigrostrial dopaminergic degradation. Recent studies showed a link between PD and deficiency of the mitochondrial NADH dehydrogenase (complex I). It has been demonstrated that administration of agents that cause complex I inhibition (such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or rotenone) induces PD-like symptoms in primates or rodents. It is, therefore, anticipated that relieving dopaminergic cells of harmful effects caused by the dysfunction of complex I may provide a novel remedy for PD. Mitochondria of Baker's yeast, Saccharomyces cerevisiae, lack complex I but instead has the rotenone-insensitive NADH dehydrogenase (Ndi1). The applicants have shown that Ndi1 restores respiratory function to complex I-deficient mammalian cells and renders the respiratory chain resistant to complex I inhibitors. In addition, Ndi1 has been successfully introduced into dopaminergic nerve rat PC12 and mouse MN9D cells without impairing their capability of differentiation. In this proposal, the applicants will employ the Ndi1 enzyme as a therapeutic tool to retard PD and investigate its potential using animal models for PD. The studies during this grant term are as follows: (1) Refinement of the optimum conditions of the Ndi1 expression in nigral dopaminergic neurons of rodents. (2) Suppression of PD's disease like symptoms in rodent models by the Ndi1 expression.